The present invention is generally directed to an encased electrical assembly, and, more specifically, to fastener detection for an encased electrical assembly.
Various electrical assemblies are encased within enclosures. For example, many automotive control assemblies include a printed circuit board (PCB) that is affixed to a housing, case or mounting structure with conductive fasteners, e.g., metal screws. In many cases, the fasteners that attach the PCB to the case, housing or mounting structure are obscured by a cover that forms a part of a final assembly, which includes the PCB installed in the case, housing or mounting structure. For example, PCBs of many automotive control assemblies may be included within a housing that includes a cover, which obscures view of the fasteners that attach the PCB to the housing. Unfortunately, in many situations when a fastener is not installed or is not properly installed an electrical failure of the control assembly may occur during operation of the assembly and its associated motor vehicle. For example, vibration during operation of the motor vehicle may cause an electrical malfunction within a control assembly due to a vibration induced intermittent open in a signal path of the control assembly.
In an effort to verify that PCB fasteners are properly installed in assemblies that may include one or more fasteners that are inaccessible or not visible when installed in an assembly, designers have produced a number of test systems to check for the presence of fasteners. For example, solenoid driven probes have been implemented within test fixtures to determine the physical presence of fasteners in a control assembly. However, such test fixtures can be expensive and in assemblies that utilize multiple PCBs, multiple test stations and/or test fixtures may be required, which add to the cost of an end product.
Thus, what is needed is a technique for determining the presence of fasteners that affix a printed circuit board (PCB) to a housing that does not require customized test fixtures for determining the presence of the fasteners. It would also be desirable for the technique to determine whether the fasteners are properly secured to the housing.
According to an embodiment of the present invention, an encased electrical assembly includes a housing, a printed circuit board (PCB) and a cover, which, when attached to the housing, obscures at least one of the conductive fasteners. The housing includes a plurality of receiving apertures and the PCB includes a plurality of securing apertures shaped to receive a conductive fastener for securing the PCB to the housing. The PCB includes a plurality of conductive traces with two of the conductive traces having first ends electrically connected to a different one of two electrical contacts that are electrically accessible from outside the housing and second ends routed to different ones of the securing apertures. Each of the remaining conductive traces are routed between a different pair of the securing apertures such that when each of the securing apertures receives a secured conductive fastener, continuity is achieved between all of the conductive traces.
Thus, according to the present invention, the presence of conductive fasteners can be determined by performing a continuity check between two electrical contacts. According to another embodiment of the present invention, the conductive fastener can be one of a machine screw, a metal screw and a bolt. According to other embodiments of the present invention, the two electrical contacts may be separate header pins or separate test points.